1. Field of Invention
The present invention relates to an electrical connection box suitable for mounting on a vehicle, such as an automobile, and is adapted to have a relatively high voltage applied to it. The invention also relates to a vehicle including such an electrical connection box.
2. Description of Related Art
Normally one secondary, i.e. rechargeable, battery having a rated voltage of 12V and a maximum nominal voltage of 14V is mounted on an automobile of the internal combustion engine type. A voltage up to a maximum of 14V is applied from the battery to a circuit composed of bus bars and the like accommodated in an electrical connection box. The power supply is distributed by the internal circuit of the electrical connection box. The operation of electric/electronic component parts mounted on the vehicle is controlled through electric wires connected with the internal circuit. On a goods vehicle, such as a lorry or truck, a rated voltage of 24V and a maximum voltage of 28V may be applied to a circuit, by a battery structure.
In recent years, electric/electronic component parts have been mounted in increasing numbers on a vehicle, and there is an increase in the electric current which is applied to one electric/electronic component part. For example, the electric power required to drive a fan has conventionally been 130 watts, but has risen to 260 watts for some fans in recent years. For a battery having a rated voltage of 12V, it is impossible to operate suction and exhaust devices of an engine, an electromotive power steering, and like devices, requiring a high voltage such as 36V. Therefore, these devices are usually mechanically operated by the driving force of the engine.
With the increase of the electric current applied to each electric/electronic component part, the diameter of the electric wires used with each component part has increased. Further, with the rapid increase in the number of electric/electronic component parts, the number of electric wires has increased recently, which has increased the diameter of a wire harness comprising a bundle of these electric wires. Consequently, the weight of the electric wires to be wired on a vehicle body has increased.
As described above, if the power supply from the battery is incapable of operating the suction and exhaust devices of the engine, they are usually mechanically operated. In this case, it is impossible to accomplish fine control of the operation of the suction and exhaust devices. Further much fuel is consumed, which pollutes the environment. Accordingly, it is preferable to operate the suction and exhaust devices of the engine and the like not mechanically, but electrically by the power supply from the battery.
In the case where the circuit is so constructed that a voltage higher than 14V can be applied to the circuit of the electrical connection box composed of bus bars and the like, it is possible to reduce the required electric current. Thus, the diameter of the electric wires and the size of a bundle of a plurality of electric wires (wire harness) may also be reduced. Therefore, it is possible to also reduce the weight of the electric wires.
Further, with the application of a high voltage to the circuit composed of bus bars and the like, it is possible to control the operation of the suction and exhaust devices, the power steering motor and other such devices electrically, in lieu of mechanically or hydraulically. In this case, it is possible to accomplish fine control of the operation of suction and exhaust devices and the like. Further, fuel consumption can be reduced, which reduces pollution.
It is preferable to apply a high voltage of about 42V to the electromotive power steering motor, the suction and exhaust devices of the engine, the fan and other devices requiring a high voltage. On the other hand, in an automobile, it is preferable to apply the rated voltage of 12V (maximum voltage: 14V) to signal-generating devices of the electric/electrical components parts and coils of relays.
However, if the electrical connection box for distributing the power supply is provided with a circuit to which a low voltage up to a maximum of 14V (28V in a truck) is applied and with a circuit to which a high voltage of about 42V is applied, a leak current is liable to be generated between the two circuits owing to the potential difference. Such a leak current may occur particularly if water or dirt enters the electrical connection box. The leak current is also liable to be generated in a circuit to which a high voltage of about 42V is applied.
A leak current is liable to be generated between adjacent bus bars in the connection box, if the distance between the bus bars is short. For instance, in the case where a high voltage is applied to one of two adjacent bus bars while a low voltage is applied to the other or in the case where two adjacent bus bars are in a circuit to which a high voltage is applied.
JP-A-6-70427 illustrates an electrical connection box in which bus bars on an insulation plate are insulated from each other by upstanding partition walls. Between the adjacent partition walls the walls of the next insulation plate above are projected downward to improve insulation in the event of water penetration.
The present invention mitigates the problem of leak currents in the connection box described above. Therefore, it is an object of the present invention to prevent generation of leak currents in an electrical connection box, particularly a connection box which is provided with a circuit to which a low voltage and a high voltage is applied, or a circuit to which a high voltage is applied.
According to one exemplary embodiment of the present invention an electrical connection box is provided having a first bus bar to which a first voltage is applied during use and a second bus bar to which a second voltage not lower than the first voltage and not more than 200V is applied during use. The electrical connection box also has a first insulation plate on which both the first and second bus bars are mounted and a second insulation plate superimposed on the first insulation plate.
The first insulation plate provides, at least at a region where the first and second bus bars are adjacent, groove structures in which the first and second bus bars are respectively received. Each groove structure is defined by a base wall surface on which the respective bus bar is disposed and a pair of opposed upstanding side wall surfaces. The first insulation plate further provides a concavity in the form of a downward recess or a throughhole located between the groove structures. The second insulation plate has a downward projection received in the concavity, the downward projection having a lower end which is located at a level lower than the base wall surface of the groove structures.
The invention is applicable for example when the first voltage (low voltage) is 14V or 28V, e.g. the nominal maximum voltage rating of a battery, and the second voltage (high voltage) is up to 200V, e.g. 42V.
In one embodiment of the present invention, a low-voltage bus bar and a high-voltage bus bar are adjacently disposed on the first insulation plate, or two high-voltage bus bars are adjacently disposed thereon, and the bus bars are shielded by the insulation material between the groove structures. Thus it is possible to prevent or minimize the generation of leak currents. The downward projection of the second insulation plate formed of insulation material lies between the groove structures in the recess or through-hole and projects downward to a position lower than the bottom surface of the bus bars.
The height of the upper insulation plate above the lower plate can be fixed by the engagement of the plates to form an air insulation zone in each groove structure above the bus bar. Thus air insulation is possible. In this case, even though different voltage bus bars are adjacently disposed or two high-voltage bus bars are adjacently disposed, the air insulation zones are partitioned by the downward projection of the upper insulation plate. This helps to prevent leak currents from being generated between the bus bars. The groove structure may be closed by the upper insulation plate to form a closed air insulation zone.
In a first embodiment, the groove structure is provided by upstanding walls on the first insulation plate. In a second embodiment, the groove structure is provided by a groove in a main face of the first insulation plate. In the latter case, the bus bars, at least where they are adjacent to each other, may be bent to provide downward stepped portions disposed on lower bottom surface portions of the grooves.
It is preferable that the high voltage to be applied to the second (high-voltage) bus bar is about 42V. This is partly because it is easy to obtain a maximum nominal voltage of 42V by connecting in series three batteries each having a rated voltage of 12V (nominal maximum voltage: 14V) of the type conventionally used in an automobile. It is also possible to use a single battery having a maximum voltage of 42V. A maximum voltage of 42V is also preferable because using a voltage close to 50V or above for the high-voltage bus bar is possibly dangerous.
The present applicants have conducted salt water experiments in order to ascertain the degree of risk when applying a voltage of 42V in an electrical junction box suitable for use in an automobile engine compartment, as follows:
1 ml of salt water was injected into each terminal hole of the casing of a junction box which had bus bars disposed inside. Electrical components such as a relay, fuse and connectors etc. were mounted on the casing. A voltage of 42V was applied to the bus bars of the junction box for 8 hours and suspended for 16 hours. This was repeated twice. There was initially no change to the bus bars and electrical components. After the third repetition, it was found that extra electric current passed between the bus bars generating heat and a portion of the bus bars melted. The heat also melted resin around bus bars such as an insulation plate, casing and resin portion of electrical components adjacent to the casing. Accordingly, since damage did not occur until after the third exposure to salt water, it was confirmed that in consideration of conditions under normal use of an automobile, the application of the electric power at 42V to the electric/electronic component parts should not cause a problem.